1. Field of the Invention
The present invention relates to coinjection stretch blow molded containers with greatly improved impact delamination resistance, which have good gas barrier properties against oxygen, carbon dioxide gas and others, good moisture-proofness, good aroma retentivity, good flavor barrier properties and good appearance, and which are used as containers for drinks, foods, and cosmetics, for example.
2. Description of the Background
Thermoplastic polyester (PES) containers as produced through stretch blow molding have various excellent properties including good transparency, good mechanical characteristics and good flavor barrier properties, and are sanitary and safe for daily use as releasing few residual monomers and other harmful additives. Therefore, they have many applications in various fields. However, since their gas barrier properties are not always satisfactory, drinks, foods and others in them could be stored only a relatively short period of time.
In order to overcome the drawback, various methods of combining a thermoplastic polyester with an ethylene-vinyl alcohol copolymer (EVOH) with good gas barrier properties to give laminated structures have heretofore been proposed. Prior to stretch blowing, a parison is first formed. For forming the parison, one may use coinjection molding, coextrusion molding, multi-stage injection molding, for example. Of these, coinjection molding is characterized by being effected in simple a apparatus, yielding few scraps, such as trimmings and others, and that the moldings produced may have a structure with an EVOH layer completely covered with a PES layer or the like and therefore, even though the moldings have no adhesive resin (Ad) layer between the EVOH layer and the PES layer or the like, they could be well multi-layered containers with seemingly good appearance owing to the adhesion effect of the ambient atmospheric pressure.
However, when conventional containers filled with drinks, foods and others are shocked, for example, by dropping them, the PES layer and the EVOH layer constituting them are easily delaminated, thereby worsening the appearance of the containers. Due to this problem, coinjection molded containers with an Ad layer-having structure of PES/Ad/EVOH/Ad/PES (see JP-A-56-501040), those with an Ad layer-having structure of PES/Ad/EVOH/Ad/PES/Ad/EVOH/Ad/PES (see JP-A-50-135169, JP-A-61-152411, JP-A-61-152412, JP-A-61-259944) and the like have been investigated. However, the equipment for producing such containers is often extremely complicated, and, in addition, controlling the thickness of each layer constituting them is often difficult. Therefore, these containers are inferior to others having no Ad layer in view of production costs and productivity.
Other methods have also been investigated of blending EVOH and other resins for increasing the delamination resistance of containers with no Ad layer. For example, in JP-A-1-176554, a method of blending EVOH with a polyamide-ester type thermoplastic resin is disclosed. In JP-A-1-182023, a method of blending EVOH with a metal-containing polyester type thermoplastic resin is disclosed. Finally, in JP-A-3-175032, a method of blending EVOH with a thermoplastic polyurethane is disclosed. However, blending EVOH with such other resins producing containers lowers the transparency of the containers produced, consequently, the containers have extremely bad appearance. In addition, the blending increases the production costs, and, depending on the type of the resins to be blended, other problems, such as poor melt stability of the blends, occur.
In JP-A-3-175033, a method is described of adding at least one salt selected from titanium salts, cobalt salts, manganese salts, antimony salts and germanium salts to EVOH for increasing delamination resistance of containers with no Ad layer. However, this method is still problematic in that the effect of a such a metal salt as used therein for improving the delamination resistance of containers is not satisfactory and, in addition, the melt stability of EVOH with the metal salt added thereto is lowered.
In JP-A-1-204736, a method is described of blending an essential component of EVOH with a minor component of EVOH for increasing the delamination resistance of containers with no Ad layer, in which the minor component EVOH has a larger ethylene content, a lower degree of saponification, a lower melting point and a larger melt index than the essential component EVOH. However, blending two different types of EVOH, between which the difference in the ethylene content is 30 mol % or more, as in Examples of the publication, lowers the transparency of the containers produced, and the containers will have extremely bed appearance. In addition, the blending increases the production costs, and, causes the problem that the melt stability of the blends is poor. This is described in Comparative Example 9 of this application.
Accordingly, it is an object of the present invention to provide multi-layered containers with good transparency and good gas barrier properties, which are produced through stretch blow molding of a parison as prepared by coinjection molding of a polyester resin and an EVOH resin, and in which the interlayer delamination under shock is prevented even though the containers have no adhesive resin layer.
The present inventors have studied the production of multi-layered containers through coinjection molding and have prepared a multi-layered parison (preform) having a structure that contains a polyester resin layer and an EVOH layer with the former being in direct contact with the both surfaces of the latter, followed by stretch blow molding of the resulting multi-layered parison into a container, for which we have assiduously investigated the resins to tee selected, the molding and working conditions to be employed and others, for the purpose of preventing the interlayer delamination between the EVOH layer and the polyester resin layer in the containers produced, when they are shocked.
As a result, it has been surprisingly discovered that a coinjection stretch blow molded container, which contains a thermoplastic polyester layer (layer a) and an ethylene-vinyl alcohol copolymer layer (layer b), with the layer a being kept in direct contact with the both surfaces of the layer b, and in which the ethylene-vinyl alcohol copolymer satisfies the following formulae (1) and (2) and its differential scanning calorimetry (DSC) gives a single peak for crystal fusion, and, moreover, has excellent impact delamination resistance:
25xe2x89xa6ETbxe2x89xa648xe2x80x83xe2x80x83(1)
92xe2x89xa6SDbxe2x89xa699xe2x80x83xe2x80x83(2)
wherein;
ETb indicates the ethylene content (mol %) of the ethylene-vinyl alcohol copolymer, and
SDb indicates the degree of saponification (%) of the ethylene-vinyl alcohol copolymer.
It has also surprisingly been discovered that a coinjection stretch blow Its molded container, which contains a thermoplastic polyester layer (layer a) and an ethylene-vinyl alcohol copolymer layer (layer b), with the layer a being kept in direct contact with the both surfaces of the layer b, and in which the X-ray photoelectron spectroscopy (XPS) of the surface of the layer b as exposed by peeling the layers a and b of the body of the container at their interface gives a pattern that satisfies the following formula (3), also has excellent impact delamination resistance:
0.015xe2x89xa6PC/(PA+PB+PC)xe2x89xa60.3xe2x80x83xe2x80x83(3)
wherein;
PA indicates the area of the highest peak (peak A) of the peaks for the binding energy of C is electrons,
PB indicates the area of the peak (peak B) appearing in the side higher by from about 1.1 to 1.8 eV than the position of the peak A, and
PC indicates the area of the peak (peak C) appearing in the side higher by from about 3.6 to 4.3 eV than the position of the peak A.